What is DOHC?

What does DOHC mean?
DOHC or Double Overhead Camshaft refers to the car engine’s valve train with two camshafts. This valve train layout or configuration is common in cars today, replacing the previous version – SOHC or Single Overhead Camshaft. Engines with the DOHC layout are said to generate more power and increase fuel efficiency.

DOHC engines allow for multiple valves in a cylinder and are specifically designed to increase engine efficiency. The double camshafts of a DOHC configuration maximize the engine’s output through the multiple valves setup, without any increase in the overall volume. But many credit the DOHC engine’s improved performance on the valve placement rather on the quantity or number. Since the intake valves are placed opposite the exhaust valves, DOHC engines are said to function optimally thereby increasing horsepower. The setup of the valves also allows the flow of gas and air in the combustion chamber more efficiently.

When compared with the pushrod design of older OHV (overhead valves), DOHC engines will result to less friction and few moving parts. OHV or overhead valves have the camshafts placed inside the engine block and the valves move by means of pushrods or rocker arms. This setup has been successfully used for many years in the past because of its simple design and durability. The only major disadvantage of the OHV engine is on the difficulty in controlling the valve timing. In contrast, DOHC’s camshafts are placed on cylinder heads, and thereby limiting the moving parts and eliminating the use of pushrods. Because of this setup, DOHC engines allow for variable valve timing on exhaust and intake valves.

Since DOHC has a more complex design and uses multiple valves, this type of configuration is more expensive to maintain. But cars today usually have this engine configuration, as DOHC is considered new and high-tech.

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About This Post
Posted by Erwin Z
on Feb 14th, 2011 and filed under Mechanics.
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